Wednesday, December 31, 2014

Trr Testing in High Voltage Diodes - to Mil Specs

During the research phase of a project I was working on, I came across a public domain Mil-Std method for testing reverse recovery time(Trr) in high voltage diodes.

What was interesting was the number of conditions the test looked for, including jitter, soft knee(rounded transition), slope, drift, double break, double trace, discontinuity, and snap-back.

Of particular interest to me was, years ago, I would occasionally see the Vbr of a DUT snap back. That usually meant a junction arced.  You could see it on the oscilloscope.  Usually the remaining junctions could withstand the same applied voltage because the reverse current was limited, thus limiting the heat dissipation.  Otherwise, the diode would have gone into thermal runaway.

Anyway, below are a few generic graphs illustrating some of the more interesting reverse voltage breakdown failure modes.



During Trr testing, VMI tests for all of the above conditions, and more.  100% of VMI diodes are Trr tested.  It is not a sample test.  It's part of our total commitment to quality,  

Tuesday, December 30, 2014

Voltage Multipliers Inc. - Holiday Schedule

Here in the States, Halloween, Thanksgiving, Hannukah, and Christmas are over.

Looking forward to New Year's, VMI will be closed January 1, 2015.

A reduced crew will be here January 2, 201 - a Friday.

We'll be back in full swing on Monday, January 5th.

In the meantime, have a Happy New Year!

May you find peace, happiness, health, and prosperity in the coming years.


Friday, December 26, 2014

New 50kV Optocoupler - Coming Soon

Look for VMI's upcoming high voltage optocoupler in 2015.

Featuring a reverse standoff voltage of 50kV (yes, 50kV), it will be slightly larger than the 15kV OC150.

Encapsulated in optically clear material, the OC50 will feature high voltage isolation, stable high voltage gain, and will be RoHS compliant.

Look for it in 2015.
15kV Optocoupler.  Coming soon - the 50kV OC50!

In the meantime, if you need a high voltage optocoupler between 2.5kV and 25kV, check out VMI's product line.


Thursday, December 11, 2014

Environmental Policy Promotes High Voltage Diode Availability

Image Credit


It’s time to renew our annual Safety Training certifications. Every employee is required to read and understand safety procedures related to the performance of his or her job.

Depending on your job description there may be a few procedures to learn, or there may be many. I just completed mine, so I’m good to go, and happy to have completed the training.  

Because of the business VMI is in - manufacturing high voltage diodes and assemblies - safety issues can be closely linked to environmental issues.

VMI uses many different materials in many different processes.

In a recent meeting VMI’s policy on manufacturing environmental issues came up.  It wasn't the primary focus of the meeting, but it was clearly a priority.  

To summarize, VMI works very hard to stay within local city, county, and state guidelines. VMI has long demonstrated a strong commitment to environmental concerns by its proactive attitude, providing dedicated resources, and following up with actions and procedures. VMI goes the extra mile by doing the right thing, by exceeding the level of expected compliance. For instance, VMI’s goal is not to keep emissions at the maximum allowable level, VMI’s goal is to eliminate them.

Why? Because we can, because it’s sustainable, and because, in the long run, it’s the right thing to do.  

VMI has been around for more than 35 years.  Sustainability in practices, procedures, and manufacturing promotes continued longevity.  The long-term gains far exceed  short-term gains.  We're in it for the long haul.      

I love a company that walks the talk!

Wednesday, December 10, 2014

How Did the End of the Semester Become the Best?



Image Credit
The semester is just about over.  The Basic Electronics class I teach at the local Junior College is just wrapping up.  All that’s left is the final exam.  The material covered everything from Ohm’s law, caps, resistors, diodes, and inductors, up to and including semi-conductors.  As is typical with college classes, we could have spent twice as much time covering the material, but alas, time was short.

The last two labs were dedicated to the "culminating experience".  The assignment was to build and debug a circuit using the 555 timer.  The timer is used to control two flashing LEDs.  
The students struggled a little – many had never soldered before – but they clearly demonstrated a grasp of the concepts presented in class.  During the last class, there were lots of discussions about resistors, ratios, current ratings, pin-outs, Ohm’s law, and strategies for debugging the printed circuit board when things didn’t go exactly as planned. 

The students encountered just about every possible scenario from the manufacturing world.  There were cold solder joints, oxidized pads, mislabeled components, and even WRONG components (I’m still trying to figure out how that happened). 

The really cool part of the whole experience was seeing those ear-to-ear smiles when they finally got their project to work.  All their hard work paid off – in SMILES. 
That's what it's all about.  

Tuesday, December 9, 2014

3 Things You Don't Want to Hear About Stressful Holidays


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The holidays are always a special time of year.  For some, that’s great, for others, well, not so much.

I hope you find yourself in the first category, but for those of us who don’t, here are a few things I’ve incorporated in the last year to help make the holidays a little happier –

1.      Don’t stress about trying to please everyone.  It isn’t going to happen.  You can please some of the people some of the time.  You can’t be in two places at the same time, so prioritize the best you can.  Blended families, in-laws, dysfunctional families (admit it, every family has at least one “difficult” family member), impossible schedules…..Maybe you’re on the flip side – a small family, or no family, and want a big celebration.  Do your best, and don’t berate yourself if you don’t get it perfect. 

2.      Re-examine those expectations.  Do you really have any control over whether Aunt Edna limits herself to two glasses of wine, or whether Cousin Sue recites the entire dialog of “Forrest Gump” at the table?  In case you’re wondering, the answers are "No", and "No".  Don’t stress.  You'll get another opportunity to do it differently next time.     

3.      Plan ahead, and know that travel delays and snow storms, are gonna happen. 
 
At work, I’ve come to expect that things will either slow down to a snail’s pace because people are out, or it accelerates to beyond unbelievable because people are out.  It just all depends.  It helps to keep a clear perspective.  There are always exceptions, but most things are not as ‘urgent’ as we’d like to believe.  Ask yourself if what you’re working on is truly urgent.  If yes, take a deep breath and keep working.  If not, well, take a deep breath and keep working, and rest a little easier knowing that that sense of urgency is just that – a sense.      

I've come to believe the key to a happy holiday is to stay calm and stress-free.  A lot of the pressure we feel is self-induced.  Learning to recognize it can help keep us healthy, and happy.   

Happy, Healthy, Holidays! 




Friday, December 5, 2014

How Right Can Holidays Go?



Happy Holidays! To You and Your Family


Happy Holidays from Voltage Multipliers Inc.



VMI will be closed for the Christmas holiday on Wednesday and Thursday, December 24th and 25th. Some of us will be back in the office on Friday, Dec. 26th.

We will also be closed Dec. 31st and January 1st, 2015 in order to start the new year off right.

Wishing you happiness, health, and prosperity, in the new year ahead, May everything 'go right' for you during the holidays!

Sincerely, Team VMI

Thursday, November 6, 2014

Four Things You Should Know About Voltage Multipliers Inc.

The next time you get an X-ray at the doctor or dentist’s office, there is a very good chance there’s a VMI high voltage diode within the machine.- Nicola Wissler
VMI made the front page of the Visalia Chamber of Commerce's November publication!

The article does a great job on summarizing what makes VMI so successful, after all, we've been around for more than 30 years, and highlights company practices to ensure future success.
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Here are a few things you may not know about Voltage Multipliers, Inc. -

1.  VMI was founded in 1980
2.  VMI is the only surviving high voltage diode manufacturer in the United States.
3.  VMI products are sold to over 400 customers, worldwide.
4.  Three things VMI attributes to their staying power -

  • Focus on high quality products
  • Realistic product pricing
  • Attracting and keeping an exceptional group of employees

Check out the full article.


Wednesday, November 5, 2014

200°C High Voltage Diode - A New Twist on a 5kV Industry Workhorse!


Not much looks different from the outside, but on the inside, VMI's Z50FF3LLHT diode has been ruggedized for high temperature, high voltage operations.

Z50FF3LLHT High Voltage, High Temp, 5kV, Hyper-fast, Diode

What's Different?


Specially selected and targeted wafers are used to minimize voltage stresses in the diode. The selected wafers perform well under higher operating temperature extremes.

Electrical Specs

Operating Temperatures:  -65°C to +175°C
Storage Temperatures:  -65°C to +200°C

Vrwm = 5kV
Io = 800mA
Trr = 30ns

More Features

The Z50FF3LLHT still features formed lead diodes for higher current-carrying capacity.


A Trr of 30ns means it has a super fast reverse recovery time - less time to dissipate power during the transition from forward conduction mode to reverse voltage blocking mode.

The Z50FF3LLHT is hermetically sealed, so you don't have to worry about moisture or ESD sensitivity.


All in all, the Z50FF3LLHT diode is robust and sturdy. Exactly the characteristics you need for down-hole or military grade applications.


Samples


Contact VMI for free samples, or to discuss your application.

Z50FF3LLHT Data Sheet

Tuesday, October 28, 2014

3 Reasons the SMF6533 5kV Diode Makes the World a Better Place

The SMF6533 5kV diode is one of VMI's most popular devices.  It offers several advantages over the axial-leaded 1N6533, which it is based.

Hermetically Sealed

The thing that this writer really likes about the SMF6533 is that it uses the hermetically sealed diode (1N6533), over-molds it with a rigid epoxy, and then forms and trims the leads.  You get hermeticity in a plastic. surface mount package.  This can be a big deal if you're running the diodes in a dielectric fluid.

Reduced Hand-assembly, Pick-and-Placeable
SMF6533

An added bonus, because it's over-molded, is the fact that the body is smooth, and pick-and-placeable.  That means reduced hand assembly, which is a big deal if you've ever worked with a combination of through-hole and surface mount devices on the same printed circuit board.  Most customers specify the tape-and-reel packaging option which makes automatic insertion even easier.

What's Not to Like?

So basically, the SMF6533 makes the world a better place because you can place it in your assemblies faster, it reduces hand assembly, and it saves you time AND money.  Plus, you get the reliability of a hermetically sealed, glass-body diode in a plastic package.  What's not to like about that?

Other voltage, current and Trr ratings are available in the same package style, offering the same advantages.  More info.

Tuesday, October 21, 2014

Cleaning High Voltage Rectifier Assemblies the Right Way

Cleaning high voltage rectifier assemblies can be a big deal! There are environmental concerns (VOC limits), safety concerns (vapors), contamination concerns, process compatibility concerns, and well, there's always the question about just how well the cleaning process works.  

Process Compatibility
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Some ICs, components, and diodes are susceptible to moisture absorption. VMI’s glass body diodes are not.

Epoxy diodes are not hermetically sealed. They are resistant to moisture, but given enough time, temperature, or pressure, they can be affected. That’s why it’s a good idea to use hermetically sealed diodes in wet environments.

But anyway, back to cleaning rectifier assemblies….it’s especially important to clean assemblies that are going to be potted. Cleanliness means the encapsulation material will better bond to any surfaces. Contamination on component bodies or along pcbs or substrates, may cause a weak spot in the adhesion, resulting in less-than-ideal voltage isolation and higher voltage stress. Higher voltage stresses can impact long term reliability, so it’s very important to have a good – very good – cleaning process.

Sources of Contamination

Lots of things can be sources of contamination. Skin, hair, chipped fingernail polish, skin oil, machine oil, dust, dirt, the presence of silicone, silicone oil used in pumps to pull vacuums….they’re all possible sources. A good cleaning system will get rid of most of the above, and what it can’t fix can be handled in other ways.

True Story

Once, long, long ago, this writer was working on a hi-rel, high visibility project. It was a product type VMI had a lot of experience building, but it was pushing the envelope on mechanical stresses of some rather large capacitors. The parts kept failing temp cycle. A failure analysis determined that the capacitors were fracturing right at the second potting line in a multi-step potting process.  It was so bad, our customer's customer showed up to help us find the problem.  (In actuality, they were very helpful).  

 Further examination revealed uncured potting materials at the interface. Even further examination determined that the proper cure schedule for the glue used to attach pads to the caps was not being followed. The pads were mechanical buffers used to keep the caps from fracturing. Not following the recommended cure schedule resulted in out gassing of the glue during the heated cure schedule that wreaked havoc at the potting interface. The out gassing contaminated the potting layer, and inhibited the cross-linking process. Once the cure schedule was followed, the problems went away.  It was an easy fix.  That is precisely why it was so embarrassing.  It only took our customer's customer showing up to shed light on the problem.  Sometimes it helps to have an extra set of objective eyes looking at the problem.  Once we got over our initial embarrassment, we went about the business of making things better, including a corrective action to prevent that same thing from ever happening again.  So far it hasn't.      

What to Look For

Some things to look for in a cleaning system include how well it removes solder solids, flux, oils, and other surface contaminants. How FAST does it work? Does it have to heat the parts to get them really clean? Does it give off any volatile organic compounds? If yes, how much? And how does much does this magic cleaning solution cost? Some of them can be quite expensive. But sometimes, it’s totally worth the cost.


What are some of your weird “cleaning” experiences?

Thursday, October 2, 2014

Sweet Consequences in High Voltage Manufacturing


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Lately it seems the word "consequences" has a negative connotation.  Well, such is not the case this time!  This time, the consequences are sweet.

September 2014 turned out to be VMI’s biggest booking and shipping month EVER (knock on wood).

Everyone worked very hard to make it happen. I mean everyone – the folks in incoming inspection, production assembly, production testing, diode assembly, diode testing, potting, maintenance, engineering, QA, sales, shipping, machine shops, drafting, purchasing, accounting, HR, management and non-management alike.  From the guys and gals who empty the trash and clean out refrigerators, to production support engineers, to lead-people, temp employees, and shift supervisors.   

As is customary at VMI, the first Friday following a record-setting month, VMI provides pizza and sodas for all during the (extended) lunch hour.  For everyone.     

This Friday we can celebrate our success and prosperity with a full belly and smiles all around.  It's a great way to lead up to the weekend, no?

Go Team!!

Wednesday, October 1, 2014

Thermal Resistance in High Voltage Rectifiers - Part IV

In Part III, we discussed using alumina substrates, formed lead and surface mount diodes as ways to achieve higher thermal transfer, and to keep parts running cooler. Regardless of the type of assembly - axial-leaded, surface mount, substrate, or pcb - one of the most important things to consider is how to CLEAN them. 

Sources of Contamination

Contaminants can range from flux residue, flux solids, to wire clippings, or even fingernail clippings.  Yes, it happened - many, many years ago - and resulted in better assembly practices overall which are now standard.  Solvents work great, but there is increasing pressure from environmental groups and government agencies to reduce VOC. That’s nothing new to manufacturing companies in the U.S. Remember the good ol’ days of MEK? Great stuff. Just toxic. 

Methods of Cleaning Rectifier Assemblies

Nowdays there are many suitable replacements that work well and are not toxic to the environment. Coupled with no-clean solders that have improved over time, cleaning rectifiers has become easy to achieve. Several methods are available, including vapor degreasers and aqueous systems. Both are suitable for certain product lines. 

Post-Cleaning Bake-out

Another source of contamination is that of cleaning material absorption. Have you ever found yourself in a situation where potting material didn’t adhere to a component because of the presence of water? Or maybe the water or solvent absorbed during the cleaning process prevented the potting material from curing. Post cleaning bake-outs can be used to drive out any trapped water or solvents. Depending on the mass of the device and other factors like maximum temperature rating on components, VMI generally starts with one hour at 100C.   Review the maximum storage temperature ratings for ALL the components.  (One time there was an issue with a capacitor where the curing temperature of the potting material exceeded the storage temperature of the cap.  It resulted in a circuit redesign and delayed delivery, but in the end, it turned out okay).   

Impact of Inhibited Cure or Adhesion 
One Example of a Vapor Degreaser

Cleanliness of a rectifier, or lack of it, can impact adhesion or curing of encapsulation materials. Adhesion of encapsulation materials to diode leads, diode bodies, substrates, and pcbs can be critical in high voltage applications. Many applications rely on encapsulation to provide additional voltage isolation between components, or between mponents and the ‘outside world’.   

Cleaning an assembly prior to encapsulation can have a huge impact on long and short term reliability.  Cleanliness won't save a bad design, but it can help prevent a good design from going bad.   

VMI works very hard to stay green. Our cleaning processes use methods and materials that are effective and environmentally safe. We’re very proud of that. Coming up in Part V is “rectifier testing”.



Tuesday, September 23, 2014

Thermal Reistance in Rectifier Assemblies - Part III



In Part II we discussed the different characteristics of commonly used materials in rectifier assemblies.  In this post, we'll look at using an alumina substrate to support a rectifier assembly using surface mount components.

 

Alumina Substrates

Alumina substrates work great with surface mount or formed lead diodes. 

Advantages

Alumina substrates offer the advantage of higher thermal conductivity than typical FR-4 fiberglass board, the kind commonly found in computers, which helps keep the components running cool.   

The rigidity of alumina means it can provide more support for components without flexing or breaking them.  Wire bonds made to an alumina substrate are less subjected to thermal expansions and contractions compared to a printed circuit board.  When the wire is less than half a mil in diameter, board flexing can be a concern.   

Alumina’s low CTE also means it is compatible with many types of encapsulation materials, AND it provides greater voltage isolation over regular printed circuit boards.  A properly selected encapsulation material will adhere well to the substrate, which improves isolation voltages between terminals, nodes, components, and the outside world.    
Integrating passive components can be a cost saver.  Capacitors and resistors can be screen-printed onto the substrate, thereby reducing real estate and interconnections where space is at a premium.   

Besides wire bonds and soldering, conductive epoxy works well with alumina too.

Alumina can attached to a metal base plate by solder or conductive epoxy.  This will help get the heat out of the assembly even faster, and because alumina’s CTE more closely matches that of aluminum, there is less chance for thermally induced mechanical stresses. 

If that isn’t enough, direct-bond copper alumina substrate is a product that bonds copper directly to alumina, which increases the thermal conductity even more than regular alumina.  The trade-off is cost (once again).  And weight.  Direct-bond copper (DBC) weighs more, thanks to the amount of copper traces present.

Trade-offs

So why not use alumina for everything?  I’ll give you a hint.  It’s a four-letter word.  C-O-S-T.
The disadvantage of using alumina over FR-4 board is that it costs more.  Direct comparisons are hard to come by, but for about the same size, an alumina substrate can be four or more times the cost of a double-sided pcb.  Cost driving factors in a substrate include thickness, length, and width.  Drilling, plating, thick or thin films, and printing resistors or capacitors, are all cost adders.

When it comes down to it, one must weigh the cost-benefit of using alumina for each application.  It works very well in high-rel applications, but is less suited for high volume consumer applications that are cost sensitive.

Up next are cleaning processes in rectifier designs, and what to look for.

Thursday, September 11, 2014

Thermal Resistance in Rectifier Assemblies – Part 2

In Part One
Metal Heat Sinks
the focus was on adding heat sinking capabilities to high voltage discrete diodes assembled in a rectifier package.

When it comes to high voltage, higher power applications, additional cooling strategies, above and beyond heat sinks attached to diode leads, may be needed.  

Axial-leaded Diodes and Copper Heat Sinks

In the case of axial-leaded diodes with attached copper heat sinks, cooling can be enhanced by suspending the diode assembly over an aluminum mounting plate and encapsulating the entire assembly.

Pros and Cons

This approach provides an increased area with which to dissipate heat. The disadvantage is, one must take care to avoid positioning the assembly too close to the base plate, especially if the base plate is grounded. If the assembly is too close to the base plate, voltage isolation through the encapsulation material will be over-stressed. When encapsulation material is over-stressed, arcs can occur between high voltage components and the (usually) grounded base plate.

High Voltage SMD Diodes and Alumina Substrates

A second approach uses surface mount or formed lead diodes soldered directly to an alumina substrate.  Sometimes direct-bond copper is used, other times, a pattern of component pads and conductors are printed on a substrate, which is then fired at a high temperature.

Once the substrate is populated, it is attached to a mounting plate, which is usually metal.  The connection is made using solder or non-electrically-conductive thermally conductive epoxy.  Next, the whole assembly is encapsulated. All that’s visible from the outside is the base plate.
Direct-Bond-Copper Substrate


Pros and Cons

Copper or aluminum are common base plate materials. Aluminum more closely matches the thermal conductivity of alumina, but neither conducts heat as efficiently as copper.  Aluminum has the advantages of being less expensive than copper, and weighs considerably less.

Properties of Aluminum, Alumina, and Copper


Below is a table listing properties for alumina, aluminum, and copper.   

Alumina 96%
  • CTE  =  6.4ppm/°C
  • Thermal Conductivity (σ) = 0.89W/In°C
Aluminum 6061T6
  • CTE = 23.5 ppm/C
  • Thermal Conductivity (σ) =  3.960W/In°C
Copper OFC

  • CTE = 17 ppm/°C
  • Thermal Conductivity (σ) = 10.00W/In°C

In Part III we’ll discuss electrical and mechanical issues when using alumina substrates and aluminum base plates.

Thursday, September 4, 2014

High Voltage Rectifier Assemblies - Thermal Characteristics and Design Tips - Part 1

Thermal Resistance in Rectifier Assemblies


Are you interested in thermal resistance or conductance in high voltage rectifiers or assemblies? Over the next several posts we'll present design information, trade-offs, and process tips on using discrete high voltage diodes in assemblies.

High Voltage Diodes - The Building Blocks for Rectifier Assemblies


High voltage rectifiers, stacks, single- and three-phase bridges have one thing in common. They all use multiple diodes assembled together in one package.  Really high voltages may require several multi-junction diodes per leg which can impact heat transfer in the assembly, as a whole. 

Kandinsky
Kandinsky - On White II 

Heat Dissipation in a High Voltage Diode

In a multi-junction glass-body diode most of the heat is dissipated through the leads. Glass is used to prevent arcing between the closely spaced silicon junctions that are approximately 10 mils thick.  This is called 'passivation'. While the Coefficient of Thermal Expansion, CTE, for glass closely matches that of silicon, glass is not a good thermal conductor. Its Thermal Conductivity, σ, is 0.031 /In°C .  Consequently, a negligible amount of heat will be transferred through the body of the diode.  The only other available heat path is through the leads.

VMI diode leads are 99.99% silver. The Thermal Conductivity of silver is 10.500 W/In°C - more than 338 times that of glass.

For that reason, most of the heat generated by impurities in the silicon junctions is transferred via the leads. That is why heat spreaders and heat sinks are added to the leads of the diodes. Since thermal transfer is proportional to the length of the heat path and inversely proportional to the cross-sectional area of the heat path, it makes sense to increase the heat dispersing area.  This is expressed by the following equation -

Thermal Impedance for Conduction = [L / (σ x A)] in units of W/In°C

Where: L is the length of the thermal path
            σ is the thermal conductivity of the material
            A is the cross-sectional area of the heath path in inches-squared

 

More than One Diode

Things start to get interesting when more diodes are added.  For instance, if you have two diodes in series and the cathode of one connects to the anode of the next via a shared copper heat sink, calculating how hot the diode junctions get can get confusing.

To simplify the calculations, we assume that the heat sink area is shared equally.  In reality, the side connected to the cathode lead will tend to run hotter than the end connected to the anode lead.  The reasons are 1)  In the forward conducting mode, junctions get progressively hotter as current enters the diode and flows through it and 2) Junctions in the center may be a little hotter than the ends because the only thermal path available to them is through the adjacent junctions.  Regardless, the differences will be small since silicon is a good thermal conductor, so average values are used. 

Lead thickness and lead materials become important, and we'll tackle that next time.     



Tuesday, September 2, 2014

3 Reasons You Should Be Thinking About Rectifier Assemblies



Slim Pack High voltage Rectifier Assembly
SP Slim Pack High Voltage Rectifier Assembly
Voltage Multipliers Inc. manufactures high voltage rectifier assemblies.  We use our own diodes in our high voltage stacks, single-phase bridges, three phase bridges, and custom assemblies.

Rectifier assemblies come in a huge array of current and voltage combinations, but most all of them have a few things in common.  First, they use VMI diodes.  Second, if there is more than one diode in the assembly, they are welded or soldered together.  Third, most all rectifier assemblies are encapsulated.  Fourth, 100% of them are tested before leaving the plant.

Reason 1  - Electrical Specification Exceed That of Discrete Diodes

Rectifier assemblies are used when discrete diodes do not offer enough isolation voltage between leads, when complex circuits are needed, or when higher reverse voltages or currents are necessary.
Encapsulation offers increased resistance to arcing between leads or to external heat sinks and ground planes.   

Encapsulation materials are chosen based on isolation voltage and thermal conductivity needed in the application.  As is often the case, selecting an encapsulation material is a matter of balancing trade-offs between thermal conductivity and isolation voltage, or thermal coefficient of expansion with cost.   

Environmental concerns must be considered too, since some potting materials (like some silicones) expand quite a bit at low temperatures, inducing mechanical stresses that can cause breakage in confined space.  

Reason 2 - Improved Thermal Conductivity

Encapsulation provides better isolation voltage, but can make thermal conductivity worse.  In situations where more thermal conductivity is needed, internal heat sinks can be added.  The downside to adding heat sinks is that most of the time the package size goes up.  To improve thermal characteristics even more, sometimes diodes are soldered directly to an alumina substrate mounted to a heat sink, and then encapsulated.  In extreme cases, rectifier assemblies use individual heat sinks attached to diodes, an alumina substrate, and an external heat sink.

How much heat sinking is right for you?  For starters, the answer to that question depends on how much space is available for your design, how much isolation voltage you need, and how hot things will run.  Let’s not forget budgets.  Cost drivers for rectifier assemblies include voltage, current, and Trr.  Higher costs are generally associated with higher voltage, higher current, and fastest Trr.

Reason 3 - Design Experts

VMI has over 90 years of combined rectifier assembly design.  We have a long history of design, while staying receptive to new materials, new methods, and our customers.  When you speak, we listen.  

The next time you have a need for a rectifier, be it a high voltage stack, 1P- or 3P bridge, or a custom assembly, give us a call.